1. Field of the Invention
The invention relates to fullerene derivates and methods of making such compounds.
2. Related Art
The extraordinary electronic properties of fullerene C60, as an n-type semiconductor with relatively high carrier mobility, have evoked continued interest to develop a wide variety of chemically modified fullerene derivatives (1-13). One of the most reliable and versatile routes to functionalization has been studied through the addition of diazo compounds to C60 (11), resulting in two isomeric products such as [5,6]-open fulleroids and [6,6]-closed methanofullerenes (2,3). From an electronic structure point of view, the [5,6]-open isomers conserve the π-electrons of the parent C60. However, they readily transform to the thermodynamically more stable [6,6]-closed isomers by thermal, electrochemical, pH and photochemical means (2, 3, 14-16), thus making their intrinsic properties in electronic applications difficult to assess.
It has been shown that 1,3-dipolar [3+2]cycloaddition of azides to C60, followed by thermal extrusion of N2 of the triazoline intermediate, leads to [1,6]-azafulleroids and [1,2]-aziridinofullerenes, respectively (18, 19). Depending on the nature of the substituents, the thermal N2 elimination affords different ratios of the two isomeric imino adducts (21-23).
Fullerene adducts have been used in organic electronic devices such as organic photovoltaics (OPVs) and organic field effect transistors (OFETs), as described in the following patents and published patent applications, the disclosures of which are all incorporated herein by reference: a) U.S. Pat. No. 7,329,709, titled: “Photoactive materials and related compounds, devices, and methods”; b) U.S. Pat. No. 6,960,782, titled: “Electronic devices with fullerene layers”; c) U.S. Pat. Nos. 6,933,436 and 6,812,399, both titled: “Photovoltaic cell”; d) U.S. Pat. No. 5,693,977, titled: “N-channel field effect transistor including a thin film fullerene”; e) U.S. Pat. No. 5,171,373, titled: “Devices involving the photo behavior of fullerenes”; f) U.S. Patent Publication No. 20070215872, titled: “Organic semiconductor material and organic device using the same”; and g) U.S. Patent Publication No. 20040016922, titled: “Electronic devices.” However, there is a continuing need to improve the electronic properties of fullerene adducts.